Hope this helps.
Thanks much, that definitely helps.
Yes, I recognize the RSAVu user interface as similar to, if not the same as, the Tek RSA that I had access to a few years ago. The SignalVu interface looks much nicer and seems to have more features.
500k complex samples with a span of 125MHz implies a best case duration of 4ms on the MDO3000 (and proportionally less at higher spans).
That isn't a ton of time, and I'd much prefer the 158ms of the MDO4000B (and calibration/correction to boot), but 4ms might be just enough to catch a signal transition of interest. What is missing to make it really useful, though, is a trigger mechanism. This seems a non-starter since there appears to be no way to trigger the RF acquisition (alas, not even through the optional digital pod).
I can see why Tek wouldn't want to risk cannibalizing MDO4000 sales by putting too much in the MDO3000, but perhaps we can hope the MDO3000 "B" might have a trigger option (such as RF power, digital pod, or protocol trigger on digital pod).
edit to add: Even if without a trigger (which would definitely be desirable), I think there is opportunity to milk the IQ data for more than just spectrum/spectrogram information. With a spectrum analyzer, one just sees a peak, and what that peak is can be a mystery. However, that same digital information can also be mined to reveal the type of modulation, the constellation size, etc., etc. It may not be measurement-grade, but it tells you more about the signal behavior.